Apparatus for tracking a moving light source

ABSTRACT

A tracking device for automatically following a moving light source that is detectable in the presence of ambient light. A carrier platform including one or more radiant energy conversion devices and a sensor array is mounted to an upright support column with a universal joint. Three independently-operated, linear actuators are equally angularly spaced about the support column with an upper end connected to the carrier platform with a universal hinge and a lower end connected to a floating base with a spherical hinge. A sensor array carried by the carrier platform includes a primary sensor associated with each actuator. During operation, when a primary sensor is not receiving direct radiant energy, the actuator retracts, and when it is receiving radiant energy directly, the actuator extends. The result is that the platform will directly track the sun across the horizon.

RELATED APPLICATION

This application claims priority of U.S. Provisional Application No.60/013,003 entitled “POINT LIGHT TRACKER” filed Dec. 12, 2007.

FIELD OF THE INVENTION

The present invention relates to tracking devices, and moreparticularly, it relates to devices that automatically maintain aspecific orientation to a light source. The present invention isdescribed in the context of a solar tracker although the physicalstructure and associated electronic control circuit have a broaderapplication than solar tracking devices. As used herein, a “lightsource” or “point light source” refers to a source of light which emitsradiant energy which is detectably greater in intensity than is ambientlight. Ambient light is all incident light at a location, particularlyall reflected light.

BACKGROUND OF THE INVENTION

In the current environment of significant human power needs, solarenergy will necessarily provide a significant contribution. One suchneed is a requirement for the conversion of solar radiation into auseable form of energy such as electrical or heat concentration usingsolar cells, for example. However, a problem lies in the capability ofsuch devices to track the sun continuously in all locations of interestand possible use, and under varying external conditions, such asweather.

Many devices are currently available that include a solar panel mountedfor movement including one or two axes of rotation. There are devicesthat have a vertical axis of rotation managed by a turret mechanism.Many devices utilize sensors to locate the desired light source. Otherdevices use heated fluids to drive the rotational movement about anaxis. However, devices that rotate about only one or two axes, arelimited in scope. They typically have a control system with a largearray of sensors to determine the position of the desired light sourceand a sophisticated electronic control system. These systems also tendto have a significantly complex or heavy frame and support structurewith a multitude of components. Turret devices require motors, gearmechanisms, chains, and bearings that can withstand heavy loads. Mostrequire setup that includes orientation sensitive to the tracked lightsource trajectory. Many tracking systems that are considered “automatic”require some sort of programming to complete the tracking sequence thatappears automatic. Regardless of the control system configuration,periodic repositioning or reprogramming is required.

SUMMARY

The tracker of the present invention includes a single support columnfixed at the lower end to the earth and having a universal joint at theupper end connecting to the center of a carrier platform. The universaljoint permits bi-axial rotation, and rotation about the third orthogonalaxis that is collinear with the longitudinal axis of the column cannotoccur. A carrier platform including energy conversion devices (e.g.solar cells) and a light source tracking array is mounted on top of thecolumn for rotational movement about two orthogonal horizontal axes sothat the platform can be positioned to face any direction from near thehorizon to the Zenith and swept 360 degrees around the axis of thecolumn. In one embodiment, the axis of the support column would passthrough the Zenith.

The orientation of said carrier platform is preferably maintained bythree linear actuators, each having one end (the upper end) mounted tothe carrier platform by a spherical hinge, and the opposing or lower endmounted to a floating base received on the support column for freesliding motion along the support axis (i.e. the axis of the supportcolumn). The lower end of the actuators (which are equally spaced) aremounted to the floating base. The floating base, confined to alongitudinal support column (but freely movable along the longitudinalaxis of the support column) secures the lower end of the linearactuators by rotating joints equally angularly spaced around the supportaxis. The floating base slides freely along the axis of the supportcolumn and maintains the mounting joints of the base of the actuators ina fixed relationship to one another and to the support axis. The mountsfor the lower ends of the linear actuators are pinned with some abilityto rotate in all directions. If screw-type linear actuators are used,the lower end of each actuator is constrained from rotating about itslongitudinal axis as in the illustrated embodiment because limitedrotary motion about the axis of extension of these actuators ispermitted due to their structure. The floating base may also providesupport and enclosure for an electronic control module for the trackingoperation.

The upper ends of the linear actuators are mounted to the bottom of thecarrier platform by an inexpensive joint which allows for rotation inall three axes at each linear actuator joint. It can also be describedas a spherical joint, rotatable in all directions over a limited butsubstantial range. The linear actuator joints are fixed to the carrierplatform and are located at equal angular spacing about, and equaldistance from the support axis which intersects with the center of thecarrier platform and is radially placed on a plane normal to thesupport. The center of the carrier platform is joined by a universaljoint to the top of the support column.

In operation, each linear actuator defines the distance between theassociated mount of that actuator to the floating base and theassociated upper hinge mounted to the carrier platform. When the linearactuators are fixed in length, the orientation of the upper platform isdefined. The plane of the upper platform may thus be adjusted (byindependently adjusting the length of the actuators) to a positionnormal to incident direct light over substantially a completehemisphere, thus enabling the platform to track the sun from sunrise tosunset at substantially all locations on earth. This is achieved byusing a minimum of three points and location of the support axis of theupper platform with respect to the support axis.

On top of the carrier platform are affixed a payload device includingconventional energy conversion modules and one control sensor arraywhich monitors the spatial location of the point light source (typicallythe sun) and controls the movement of the linear actuators to positionthe carrier platform to “face” the sun. By this it is meant that animaginary line (referred to as the sight axis) which is perpendicular tothe carrier platform, intersects both the carrier platform and thetargeted light source. The sensor array includes three primary sensors(which detect direct illumination) and three ambient light sensors, oneassociated with each primary sensor. An opaque blinder partiallyisolates the primary sensors from one another so that their respectivefields of view are equal in scope but isolated from the other primarysource sensors in such a manner that when all three primary sensorsindicate they are facing the source, the carrier platform also faces thesource (or sun).

In the disclosed control sensor array there are three sectors comprisingthe 360 degree field about the center of the sight axis. Each primarysensor is associated with an ambient sensor in such a manner that when aprimary sensor generates a signal substantially greater than theassociated ambient sensor, it is taken as an indication that the sourcesensor is receiving solar radiation directly (i.e. it “sees” the “sun”).When the sun illuminates a sensor a signal is sent to the controllerwhich reverses the current flow to the associated linear actuator. Oneend of each actuator (referred to as the base) is mounted to thefloating base and the other end of the actuator (the rod end) is mountedto the carrier panel at a location opposite to its associated primarysensor. Thus, when a primary sensor generates a signal that its sectoris receiving incident sunlight over its associated blinder, thecontroller reverses the action of the associated linear actuator. Thus,each primary sensor is moved repeatedly between a “blind” position and a“sighting” position.

A main sensor (the master sensor) is positioned in an elongated recesswhich extends along parallel to the sight axis so that when it detectsincident sunlight, it indicates that all three sector sensors aredetecting incident sunlight simultaneously. At this instant the payloador solar conversion device is also facing the sun in a position normalto the sight axis. Each linear actuator has a similar relationship toits source pair. The controller reacts instantly to the signals sent bythe control sensors for extending or retracting the linear actuators. An“all stop” circuit senses this state and stops all linear actuatorsuntil the sun moves to a position at which a primary sensor no longerdetects it then, the process is repeated to maximize the amount of timeduring the sun's availability in which the payload sights the source bybeing positioned in a plane perpendicular to the sight axis of thecarrier platform.

Each linear actuator is, during the duty cycle, either extending orretracting, simultaneously and independently of the other actuators. Thesensor's signal of the presence or absence of the sun determines whetheror not a particular actuator retracts and extends. When a control sensordetects illumination it actuates its associated actuator to extend, andwhen the sensor does not detect incident light energy, it sends a signalto its associated linear actuator to retract. The physical orientationof an actuator in the apparatus and with respect to an associated sensorcauses the cylinder to extend in the presence of light and thus orientthe carrier platform toward the source of light, causing the platform tomove generally toward the source.

The electronic controller includes a plurality of timers that manage theuser-required timed sequences of activity of the tracker, the ‘targetacquired’ all-stop circuit, and the optional ambient light system enablecircuit. The first timer considered manages the Sleep Cycle (i.e., whenno light source can be detected by any of the three control sensors).The Sleep Cycle is variable and can be set at whatever length of timerequired by the application. Generally for a sun tracker device a SleepCycle of 20 to 40 minutes is sufficient to maintain efficientorientation of the solar energy collector. If a parabolic collector isused, a shorter Sleep Cycle could be implemented. Any desired timingcycle may be set. At the end of each Sleep Cycle, the system isreactivated.

In addition to a variety of timer configurations that may be of use tothe customer, the apparatus can be placed into operation with no timers.That is to say, it can remain in “live” status and constantly sensitiveto the position of the light source. An example of this applicationwould be to have the tracker mounted on a moving vehicle. If thedirection of the vehicle changes randomly the tracker is required toadjust accordingly to reacquire the target. On the other hand, if thetracker were mounted to a slow moving vehicle like a ship or barge,timers may be of use.

The duty cycle timer manages the overall time that the linear actuatorsare active. The time needed for this activity will depend on the size ofthe tracker, the customer requirement for the speed of the tracker, andthe time it takes to acquire the target light source. A large trackerwith significant mass will take more time to orient than a small lighttracker. Additionally, each actuator has limiting devices on itsrespective extension or retraction. Consequently, the reorientation ofthe tracker will generally take only a few seconds. However, if thetiming is through the night from a sunset to a sunrise the tracker willneed to move through an angle of approximately 170 degrees to acquirethe sun. This may take 5 to 60 seconds depending on the size of thetracker. The duty cycle timer will allow for a full re-orientation ofthe device, possibly up to 60 seconds, then generate the all-stop signaland signal the sleep timer to reset.

A complete cycle may take place in seconds, thus significantly reducingthe power usage of the device. During the Sleep Cycle, very littleenergy is used to maintain the orientation of the carrier platform.Energy consumption during the duty cycle is dependent upon the forcesneeded to move the carrier platform and will vary. During the SleepCycle, the control circuit uses only enough power to maintain the sleeptimer.

When the light source is not present, the default activity of thecontroller is to force the actuators to retract. Each actuator has astop or limit device for its full extend and retract positions. In thecase of the electric screw cylinder, limit switches may be used to cutthe power to the screw motor. During a “low light” event, the actuatorsfully retract and stop, as though it were night. In this state, theplatform faces square to the zenith. The duty cycle timer will completeits cycle and the device will immediately return to its low energy stateof the global timer. With all actuators retracted, the carrier platformwill align the sensor array module central axis with the axis of thesupport column. Thus, on a cloudy day the instant tracker will retract,thus maximizing the sky solid angle and positioning the platform suchthat it is ready for the sun to come out at some other position. Atnight, the tracker goes into the retracted actuator orientation. Thisalso provides a reduced frontal area exposed to lateral winds in lowlight conditions of storms.

With the desirability of low energy consumption, memory of the lastorientation is not maintained. This is acceptable because the trackerwill always orient as needed when the sun comes out. The need for adifferentiation between low and no ambient light is minimized andtherefore ignored because of the simple relationship between sensors andactuators. In cases where ambient light detection is desired or needed,the detection of a signal of the presence of ambient light, initiatesthe first duty cycle. If the sun is available, the device willimmediately orient itself toward the sun. If no (or insufficient) sun isavailable, the device actuators remain in a fully retracted state, theduty cycle timer will complete its cycle, followed by the sleep cycletimer sequence.

The ability of the instant tracking system to achieve full frontalexposure to the sun (i.e., the Sight Axis of the platform intersects thesun) throughout the day, 365 days per year. The simple mechanicalcomponents of the invention are relatively inexpensive. Assembly andmaintenance are minimized due to the relatively few components and theuse of standard, available components, such as actuators, sensors (whichmay be photo resistors) and solar cells. The electrical control systemis modular and simply plugs in to the actuators and sensor array module.The simplicity enables an economical solution to the solar trackingindustry that will allow consumers to set up and begin using the devicealmost immediately. No special skill or training is needed in theunderstanding of one's location on the planet.

The instant device will easily track a target light source through anyspherical or celestial path. It will track the sun as easily at theArctic Circle as it will at the Equator. With the appropriate mountingkit any solar panel can be kept facing the sun directly anytime the sunshines. During cloudy days the panel will face directly upward and willgather light from the largest part of the sky at all times. For example,this would maximize the light gathering capability for a solar panel.

With a simple setup procedure, relatively low cost purchase, the returnon investment will be significantly increased beyond a lesser efficientand more expensive solar tracking device. As a solar tracking device, itwill find immediate use anywhere on earth, particularly in the higherlatitudes. Additionally, as a low maintenance device, it will need noseasonal alignment with the position of the sun at any given time. Inregions of snow and ice, the sensor array module can be displaced to anyheight above the tracking platform to ensure it is always able toacquire the sun.

There is no digital clock needed to set with month, day, and time. Whenthe sun comes up this tracker goes to work. There are no expensive partsexcept the linear actuators. All other components can be fabricated.

Other features and advantages of the present invention will beunderstood by those skilled in the art from the following detaileddescription of a preferred embodiment accompanied by the attacheddrawing in which the same parts are referred to by identical referencenumerals in the various views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an upper perspective view of the carrier platform, linearactuators and support;

FIG. 2 is a side view of the device of FIG. 1, showing hinges andactuators in a position targeting the location of the sun near thehorizon; and into the plane of the page;

FIG. 3A is a side view of a sensor array module;

FIG. 3B is an upper perspective view of the sensor array module of FIG.3A, with its protective cover removed;

FIG. 3C is an upper side perspective view similar to FIG. 3Billustrating various angles at which the sun's rays may impinge,depending on the position of the sun;

FIG. 3D is a perspective view of a sensor array with the sun directlyabove the array;

FIG. 3E is a top view of a sensor array;

FIG. 4 is an upper perspective view of the device of FIG. 1 without thecarrier platform showing the Linear Actuators, floating base and asensor array module in an adjusted position directly viewing the sun inthe position of an observer;

FIG. 5 is the block diagram of a control system (controller) for thetracker;

FIG. 6 is a schematic of a control circuit for each actuator;

FIG. 7 is a circuit schematic for the All Stop Circuit;

FIG. 8 is a logic chart illustrating the condition of the actuatorsunder various operating conditions.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

The system shown and described is able to track the target light sourcewithin a solid angle of approximately 5.2 steradians, that is, about 10degrees up from the horizon in a full 360 degrees. Consequently, it canbe used as a solar detector at almost any latitude on earth. As a solarpanel tracker, the instant system can be used from the earthly poles intheir respective summers to the Equator. Once the tracker has beeninstalled with the payload device, only power needs to be supplied. Theintegrated sensor/actuator controls will power up and orient the deviceto the direction of the target.

Referring to FIGS. 1 and 2, the device comprises a multiaxial mechanicalsystem including three linear actuators 9, 10, and 11. Each actuatorextends and retracts linearly and has a base end (11A for actuator 11,FIG. 2), and a rod end 11B. A single support column 1 supports theentire device. The support column 1 may be mounted to a stand (portable)or permanently fixed, as in concrete. At the top of the support, column1 is a universal joint 2 (FIG. 2) which is connected to the centralportion of a carrier platform on which the payload devices, such assolar panels, one of which is shown at 19 in FIG. 1, are mounted. Theuniversal joint 2 is connected to and supports the center of the carrierplatform 6. The carrier platform 6 is mounted such that it is capable oftilting in a solid angle, typically 5.2 Steradians, but can be designedfor somewhat more or less, if desired. The universal joint 2 allowsrotation of the carrier platform 6 in the two orthogonal axes normal tothe longitudinal axis of the support column 1. Consequently, the payloaddevice 8 mounted on the carrier platform 6 does not rotate about thelongitudinal axis of support column 1. It can be said to “roll” aboutthe support column 1. That is, the payload device 8 can only rotateabout two horizontal axes. Universal joint 2 allows a two-axis movement,both axes are perpendicular to the vertical axis 1A of the center column1 (which is assumed to be vertical, but which is not necessarily thecase).

Referring to FIG. 2, the universal joint 2 which connects the center ofthe carrier platform 6 to the support column 1, includes a hinge plate13A connected by a pin 13C to the top of the support column 1, andincluding ferrules receiving a second pivot pin at 13C perpendicular tothe axis of pin 12 and forming a hinge pin between hinge plate 13A and ahinge plate 13B which may be stamped out of the metal sheet from whichthe carrier platform is formed.

In the present embodiment the actuator rods of actuators 9, 10 and 11are capable of limited rotation about their axes. As a result, auniversal joint is formed between the distal ends of each of the rods ofthe actuators 9, 10 and 11 to the carrier platform 6. These joints aredesignated 9A, 10A, 11A, respectively.

Referring now to FIG. 1, a floating base 23 includes a tube 24 thatslides freely along the z-axis 1A (i.e., of the center axis supportcolumn 1) and a disc-shaped member or plate 23 that is slideablyreceived on the support column 1. The floating base 23 extendsperpendicular to the axis 1A of support column 1. The floating base 23contains sockets for the pins of pin joints 5 for the lower ends of theouter tubes linear actuators 9, 10, and 11. The linear actuators 9, 10,and 11 secure and support the floating base 23. That is, the threeactuators 9, 10, and 11 have their rod ends connected to and the carrierplatform 6 as described above which is supported by the column 1, andthe butt ends of the actuators are pinned to the floating base 23, andthey thus support the floating base 23, which is free to move up anddown on the support column 1. There is a constant load due to gravity atthe central pinned joint 13C of the carrier platform 6. All loads thatinduce rotation in the rotating axes of the central universal joint 13mounted to the central support column 1 are countered internally by theactuators 9, 10, and 11, the carrier platform 6, and the floating base23. Referring to FIG. 2, the central universal joint comprised of 13,13A, and 13B, and the central support column 1 support all verticalloads. All loads that are normal to the central support column 1 andcause bending of said column are countered structurally by the columnitself. The carrier platform 6 does not rotate about the axis 1A ofcentral column 1.

All the actuators are attached equally around the floating base with thejoints in a plane normal to the longitudinal axis of the support column.As this structure is stable and in equilibrium all the net forcesbalance out. That is to say, the sum of all the forces equal zero.Nominally, the vertical push/pull forces caused by rotation of thecarrier platform simply balance out. The floating base remains fixedvertically along the longitudinal axis of the column. Additionally,these same push/pull forces would cause the floating base to rotate awayfrom concentricity to the longitudinal axis. However, these verticalforces induced in the direction of the longitudinal axis of the columnthe floating base easily resists the moment induced by the actuatorspushing downward and upward simultaneously. The floating base includes acenter tube constrained and will remain concentric to the shape of thecolumn. The forces induced by the actuators that are in a plane normalto the longitudinal axis of the column have the vector sum of the forcesequal to zero. There is no remaining force that would cause rotationabout the longitudinal axis of the column. In summary, all the forcesthat might cause the floating base to rotate about the longitudinal axisof the column are balanced internally. The floating base will move onlyslightly to balance the net triangular shapes imposed by what isultimately a tetrahedral shape.

The linear actuators 9, 10, and 11 that are mounted to the floating base23 have multiaxial rotations at their associated pin joints 5, but haveno local displacements with respect to the floating base 23. If thefloating base 23 is rotated, it translates upward. With the effects ofgravity, the sliding actuator mount assembly 2 and all three actuators9, 10, and 11 seek the lowest point at equilibrium. The purpose of thisis to relieve any local translation away from the center axis of supportcolumn 1 at a universal joint 14 (which connects the top of the supportcolumn 1 to the center of the carrier platform, FIG. 2) that may beimposed by the rotation of the upper platform 6 due to the offset fromthe z-axis of the support column 1. The lower pinned joints 5 are spacedevenly at 120 degrees around the axis of support column 1.

Referring to FIGS. 1 and 2, a sensor array module 25 is mounted to thetop of the carrier platform 6. The sensor module (and the carrierplatform) are oriented by the movement of linear actuators 9, 10 and 11.The rod ends of the actuators are mounted on the bottom side of thecarrier platform 6 by means of the three hinges 13 as seen in FIG. 2.The upper member or plate of each of the hinges 12 is rigidly fixed tothe carrier platform 6. Each of the linear actuators 9, 10, and 11 isspaced equally at 120 degrees on both the carrier platform 6 and thefloating base 25. The lower half 13A of each universal joint 9A, 10A and11A is pinned (at 13C) to the rod of an associated actuator 11, 12, 13to provide a local (horizontal) axis of rotation about the actuator rodof the associated linear actuator 9, 10, and 11. In the illustratedembodiment, the actuator rod is mounted to a screw and may rotate easilybut within a limited range within the actuator 9, 10, or 11 barrel orhousing. Thus, there are three orthogonal axes of rotation at each upperhinge 13A, 13B and 13C. Given the screw action of the actuator rod, asimple universal joint can be used to provide the two axes of rotationnormal to the local z-axis of actuator 9, 10, and 11. Other multiaxialrotational joints may be employed so long as it restricts lateraldisplacement.

Still referring to FIG. 1, in addition to the sensor array module 25mounted to the top of the carrier platform 6, solar panels (one of whichis schematically illustrated at 19) may be mounted to the upper surfaceof the carrier platforms 6. Alternatively, the carrier platform 6 cansupport flat solar panels, parabolic reflective surfaces, arrays oflenses or any other type of surface requiring tracking capability andare referred to as the payload device 8. The carrier platform 6 providesthe mounting configurations needed and functions in a dual purpose asthe mount for the actuators and the mounts for the desired payloaddevice (e.g. solar panel).

It may be observed that the universal joints mounting the rods of thelinear actuators to the bottom of the carrier platform form a triangle,and the axes of the linear actuators intersect at a point below on theaxis of the support column 1. The four imaginary surfaces formed is atetrahedron with three triangular surfaces formed by three adjacentactuator axes, and the fourth triangle by the three spherical joints 5attached to the carrier platform.

Still referring to FIG. 1, the linear actuators 9, 10, and 11 can be ofany number of known designs. They are required to retract or extendunder a variety of loads. For larger systems carrying substantial weight(or as desired), hydraulic systems can be used. Hydraulic cylinders andpneumatic actuators are included as linear actuators.

The Sensor Array Module

The sensor array module 25 (FIG. 1) is described with reference to theFIGS. 3A-3E. The module 25 includes a base 27 on which there is mounteda blinder 31 formed of three intersecting walls 32, 33, and 34 made ofopaque material and angled 120 degrees apart so that each pair ofadjacent walls forms a sector of approximately 120 degrees. At the baseof each sector and at the intersection of the walls is a primary sensorwhich may be a photoresistor (that is, the electrical resistance varieswith the intensity of light incident on the active element of thephotoresistor). Thus, sector 45A (FIG. 3B) is associated with theprimary sensor 36 and is defined by walls 32 and 34 of the blinder 35.Similarly sector 45B is associated with primary sensor 37 located withinwalls 32 and 33, and primary sensor 38 is located in sector 45C which isdefined by walls 33 and 34.

In FIG. 3B, at the base of the sector 45A formed by intersecting walls32, 34, primary sensor 36 is located to detect light when the sun (showndiagrammatically at S) is in a range of positions. The other two primarysensors designated 37, 38, cannot directly view the sun in the positionof FIG. 3B because blinder 31 precludes direct incidence of light whenthe sun is in the sector shown in FIG. 3B and low relative to thehorizontal surface 29 of the base 27A on which the blinder and primarysensors are mounted.

As will be described in more detail, when a particular primary sensor(which is placed at the innermost and lowest position of a sector toreceive direct light from the source and is to be distinguished fromambient sensors, to be described below) such as 36 detects the lightsource, its associated actuator is energized to extend. In FIG. 3B, thisrotates the sensor base 27A toward the sun S because the associatedactuator is connected to the carrier platform outwardly of the wall 33.When a primary sensor goes dark (or is not illuminated) during normaloperation, its associated actuator retracts to rotate the carrierplatform 6 (and thus the sensor base 27A) to raise the primary sensor.This searching for the sun continues until all three primary sensorsdetect the sun directly.

At the center of the tripartite blinder 35 is an elongated opening 42which forms a cylindrical recess as seen in FIG. 3B and may have acentral axis extending parallel to or coincident with the sight axis ofthe unit. A sensor 39 is located at the bottom of recess 42. Thus, whenthe sensor 39 detects direct sunlight, it actuates an “All Stop” circuit(to be described) which de-energizes all three linear actuators becausethe sight axis of the carrier platform intersects the target.

The primary sensors are equally placed around a horizontal plane spacedapart 120 degrees and equidistant from the center of the blinder 35where the “target aligned” sensor 39 is located at the bottom ofrecessed opening 42. Each actuator is associated with a sensor paircomprising a primary sensor and an ambient sensor. Each sensor pair ismounted on base 27A at an elevated angle relative to a horizontal planeof the carrier platform 6 such that when the sight axis of the array isaligned with the zenith, the horizon will also be visible to the array.In this orientation, the true horizon is not visible to the targetingsensor. Additional sensors can be added at various angles to the arrayto increase angular sensitivity. Base 27 provides a housing for thesensors.

Ambient sensors 38A, 38B and 38C are housed within recesses formed inthe base of the outer surfaces 33A, 34A and 35A of walls 33, 34 and 35respectively. Thus, ambient sensor 38A is mounted in recess located atthe base of peripheral wall 33A of sector wall 33. The recess forambient sensor 38B is designated 34C in FIG. 3B. The base mount 23 (FIG.3B) for the sensors rises toward the center to enable the sensors to“view” the horizon for almost 360 degrees about the sight axis. Whendarkness is present, all actuators are retracted, ready for the firstsign of light.

Support columns may be tubular to allow for wiring of the sensors and itincludes a mount for the sensor array module 7. The opaque walls orseparators 32-34 limit the lateral field of view for each sensor 36, 37,and 38 to approximately 120 degrees. The ambient sensors 38A, 38B and38C monitor the reflected light produced by the light source and reflectback to the sensor module. The ambient sensors 38A, 38B and 38C are eachlocated in the opaque wall 33, opposite their respective primary sensor36, 37, and 38 respectively. The cover 26 (if used) is transparent andis rigidly mounted.

The separator walls or panels 33, 34, 35, as seen from FIG. 3E, areequally spaced at 120 degrees. The three walls 33, 34, 35 limit thefield of view of each sensor to approximately a third of the 2πSteradian solid angle of view. The height of the three panels 19 mayaffect the targeting accuracy of the device. Effectively, the accuracyof the tracking device can be enhanced by the geometric placement of thesensors, the height of the three separator walls, and, the height anddiameter of the targeting sighting recess 42. The cover 28 may be madeof a generally translucent material that transmits a desired intensityand/or wavelength(s) of light. Thus, in addition to the electroniccontrols, the cover 28 may affect sensitivity. It may also act as acover to protect the primary and ambient sensors, and the separatorwalls from the environment.

All three primary sensors 36, 37, and 38 will acquire the target lightsource when the module's vertical sight axis sensor 40 is pointed at thetarget light source. The sight axis of the sensor array is normal to theplane of the carrier platform 6. As the linear actuators 9, 10, and 11variously extend or retract, the array 7 will eventually come into aposition in which all three primary sensors 36, 37, and 38 and therecessed sensor 39 also have line-of-sight view to the target source.When all four sensors acquire the target light source an “All Stop”circuit (to be described) is enabled, and it locks the tracking panelinto position at an angle directly facing the target light source (atthe time of acquisition).

Referring now to FIGS. 3A-3E, various orientations of the target lightsource illustrate the operation of the system. FIG. 3A shows the SensorArray 7 of FIG. 1 with the shading panels generally located within thestructure of the Cover with the incident light source illuminatingvarious sensors.

FIG. 3B shows the illumination of the primary sensor 36 for onedisposition of the sensor relative to the target sources. Primary sensor36 is illuminated and its associated ambient sensor 38A is shaded. Asignificant difference in brightness is registered and the controllergenerates a signal to extend actuator 10 which has its rod coupled to alocation diagonally opposite primary sensor 36. This raises the wall 33of the blinder 35 and tilts the sensor array such that the axis of thesighting recess 42 becomes more in alignment with the diagrammatic lightray R of the source and elevating the associated ambient sensor 38Aupwardly relative to the associated primary sensor 36, thus increasingthe amount of light sensed by the ambient sensor. The other two primarysensors 37, 38 are not directly illuminated; and the controllergenerates a signal to retract their associated actuators 9, 11.Illumination of the ambient sensors strengthens the retract signal. The“target acquired” sensor 40 is not yet illuminated.

FIG. 3C shows an orientation of the array wherein two primary sensors36, 38 are illuminated by the source S located toward the bottom of thepage, and their respective ambient sensors are shaded causing the signalto extend for the two associated actuators. The third primary sensor 37is shaded while its ambient sensor 38B is directly illuminated. In thiscase, the controller generates a signal to retract the actuatorassociated with primary sensor 37. The primary sensor 37 is not yetilluminated due to the lower position of the target.

FIG. 3D shows the light source S generally overhead and aligned with thelocal Z-axis or sight axis 50 of the Sensor Array 7. In this event the“Target Acquired” sensor 40 is illuminated. The controller signals an“all stop” circuit to cease all signals to the actuators.Coincidentally, all the primary sensors will be illuminated while theassociated ambient sensors are shaded.

As the actuators independently extend and retract eventually a secondand then the third sensor 36, 37, and 38 will become directlyilluminated. When the target sensor 40 becomes illuminated (FIG. 3E),the “all-stop” signal is given. The orientation of FIG. 3C, however,shows sensors 36 and 38 as illuminated and sensors 37 and 40 as shaded.In FIG. 3E, the tracker has moved such that the recessed sensor 40 isalso illuminated and the ambient sensors are not directly illuminated.At this slight angle from vertical axis of the sensor array, sensor 40signals the all-stop. Sensor 40 is illuminated at a small solid angledefined by the diameter and length of the tubular recess in which it ismounted, and the physical size of the sensor.

The Electronic Controller

FIG. 5 is a block diagram of the electronic controller for theactuators. The coupled mechanical system (within block 54) of theapparatus shown is similar to that of FIGS. 1 and 4, which can be usedfor visual reference. The geometry in the coupled mechanical systemimage within block 54 includes the carrier platform 6 of FIG. 1. Theupper part of the diagram of FIG. 5 shows the integration of the systemsensors with the actuator enable and drive components. When voltage isapplied to the system, a Global Timer 56 generates the Sleep and Dutycycles for the apparatus. After a specified time, the timer 56 signals asingle pole single throw (SPST) relay controller 57 which, in turn,energizes a normally open relay circuit of a single pole relay 58.Electrical power from source 59 is then fed to three double pole-doublethrow (DPDT) relays 60, 61, 62 for driving the linear actuators 9, 10and 11 of FIG. 1. Each relay 60, 61, 62 is cross-wired such that ifthere is no signal from the associated actuator relay controllers 63,64, 65, activation of relays 46-47 will cause all the associatedactuators to retract. This, in turn, causes the coupled mechanicalsystem of FIG. 1 to re-orient the Sensor Array toward a horizontalposition. This activity may or may not change the incident illuminationof the associated sensors. However, in the presence of the target lightsource, the states of all sensor array sensors may change to that ofilluminated in any combination and is represented by a general sensorarray input, λ.

Lambda (λτ) inputs are defined as follows for use in FIG. 5 and FIG. 8.λτ is the source light input to the Target Sensor, λ_(1P) is the inputto the primary sensor of Actuator Primary, λ_(2P) is the light input ofthe Primary sensor of Actuator 10, λ_(3P) is the input to the Primarysensor of actuator 11, λ_(1A) is the input to the Ambient Sensor ofActuator 9, λ_(2A) is the input to the Ambient Sensor Actuator 2, λ_(3A)is the input to the Ambient Sensor of Actuator 10. These primary/ambientinputs are compared for relative brightness and the appropriate signalis sent. The Target sensor output cuts the Timer enable. The actuatorsare controlled by the outputs of the primary sensors. A high signalcauses the actuator to extend, a low signal causes it to retract.

Referring to FIG. 8, all combinations of the states of λ are described.If sensors are illuminated such that there is any combination of, λ₁,λ₂, or λ₃, it provides a signal to the associated Relay Controller,which in turn activates the associated Double Pole Double Throw relay,thus reversing the current flow to the associated actuator. Sinceillumination of a sensor causes the coupled mechanical system to seek aposition normal to the point light source and since all three sensorsare seeking the point simultaneously, the plane of the carrier platform6 moves inevitably toward an orientation normal to the position of thepoint light source.

When the carrier platform 6 approaches the position normal to the PointLight source, the Target Sensor 40 will become illuminated, λ_(T). Inthat event, a signal is sent to the normally-closed Target SignalDisconnect Circuit 67 controlling the Single Pole (SPST) Relay 58. TheSingle Pole Single Throw relay is de-energized and current is cut off toall actuators. This set of circumstances is represented by theOrientation number eight of the logic diagram of FIG. 10 and is calledthe “All Stop” state. As long as the Global timer signals the Duty cycleand the Target Sensor remains illuminated, the apparatus will remainmotionless. The targeted point light source has been acquired. As longas the Global timer signals the sleep cycle, the Single Pole SingleThrow relay remains in its normally open circuit state and no currentflows to the linear actuators 9-11 of FIG. 1.

The double pole double throw relays 60-62 are cross-wired and arereferred to as a directional controller for the associated linearactuator. These circuits control the extension or retraction of theassociated linear actuator. If a voltage is applied, current is alwayssupplied to the actuator.

In summary, the Sensor Array of the coupled mechanical apparatus isdynamically controlled by the illumination, λ, of the coupled sensors.This activity is stopped by the illumination of the Target Sensor. TheGlobal Timer provides the overriding system control timing.

The spherical hinges 9A, 10A and 11A, when mounted to the bottom of thecarrier platform 6 form an equilateral triangle in the illustratedembodiment. Other applications may require other dimensional triangulararrangements. For example, location of the hinge toward the center ofthe column 1 affects the speed with which the carrier platform rotates.The sensor array module 7 of FIG. 1 mounted on top of the payload device8 is associated with the three linear actuators 9, 10, and 11 withsimilar triangular geometry.

Primary sensors 36, 37, 38 are placed circumferentially and spaced at120 degrees around a horizontal circle. The sensor array module 7 ispreferably located on a plane parallel to the carrier platform 6. Thesensor array 7 of FIG. 1 can be placed anywhere on the payload device19.

Operation

Referring now to FIG. 4, generally, when the target light sourceilluminates a photoresistor its resistance changes, which generates asignal to force the associated linear actuator to extend. ReferencingFIG. 4, primary sensor 36 is therefore exposed to the part of the skyopposite the associated linear actuator 10. Primary sensor 7 is exposedto the part of the sky opposite the associated linear actuator 9.Primary sensor 38 is exposed to the part of the sky opposite theassociated linear actuator 11. With this arrangement, when any one ofthe linear actuators 9, 10, or 11 extends, the carrier platform 6 isrotated toward the area of the sky that is incident upon, and thusactuating, (or strengthening the signal of) the associatedphotoresistor. Each of the other two linear actuators 9, 10 of FIG. 1will operate in a similar manner but independently of any of the otheractuators. The net behavior of all linear actuators combined defines theplane of inclination to which the sensor array module is forced. Withthe movement of the carrier platform 6 eventually illuminating thecollimating sighting recess 42 which houses the central “All Stop”sensor 40 of FIG. 3, all movement of the actuators is stopped.

The system described is fully automatic and will dynamically track anintended light source regardless of the initial position and trajectoryof that light source. It can be electronically configured to beself-actuating enabling the use of the device in remote areas. Powerloss will not affect the operation once power has been regained. Thereis no electronic memory to maintain and no initial orientation isrequired.

The operation of the device is simple. The control system is completelyintegrated into the tracker mechanism. It functions automatically totrack a light source in a hemispherical trajectory. As a solar paneltracking device it preferably is placed on a vertical support, such ascolumn 1 of FIG. 1, so that the hemispherical tracking capabilitydescribed above aligns with the sky.

Other applications for the device may have other targeting needs thatrequire a central column that is not vertical and cannot be gravityenabled. Referencing FIG. 1, a simple tension spring could be used topull the sliding actuator mount 1 away from the carrier platform 6.

The basic geometry of the device is that of a set of four triangles(three formed by extending the axes of the linear actuators until theymeet on the axis 1A of the support 1, and the fourth by the mounting ofthe rod ends of the actuators to the carrier platform 6) attached atcommon points and sharing common edges, thus forming a tetrahedron. Whatmight be typically called the base (or bottom surface) of thetetrahedron has been inverted, and is supported by a column at thecenter of one of the triangles designated to be the inverted base.

Turning now to FIG. 6, there is shown a circuit schematic diagram forthe drive circuit or controller for each of the actuators 9, 10, and 11.All three drive circuits may be the same, so only one need to bedescribed for an understanding of the invention by those skilled in theart. The actuator may be the one designated 63. Actuator 63 is connectedin series with the contacts 64 of a double-pole, double-throw relay 78and a source of electrical energy M, which may be a battery associatedwith actuator 63.

The primary sensor 36 and Resistor R1 are connected in series with theassociated ambient sensor 38A and a resistor R2 which has a valuegreater than R1. The junction between R1 and R2 forms a junction or node71 which is also connected to a junction between resistors R3 and R4,and to an input 75 of a comparator circuit 72. R3 is greater than thatof R4, and the resistance of R3 and R4 are very much greater than R1 andR2. A second input 76 of the comparator 72 is connected to a junction 63between fixed resistors R5 and R6 (which may be equal in resistance).

It may be assumed that the response characteristics (i.e. incident lightversus resistance) of the photoresistors 36, 38A are equal. Inoperation, when primary sensor 36 is not receiving directly incidentlight, the values of the respective sensors 36, 38A are great incomparison to R1 and R2 and substantially equal. Thus, the voltage atnode 71 is greater than at node 73 (because R2 is greater than R1, andR5 and R6 are equal). Thus, the voltage at comparator input 75 isgreater than that at node 73 (the input 76) and the comparator 72 doesnot generate a positive signal to cause transistor 77 to conduct.

When the light source is directly exposed to the primary sensor 36, itsresistance decreases substantially, while the resistance of theassociated ambient sensor 38A remains generally constant, so that thevoltage at node 71 increases substantially relative to the constantvoltage at node 73, causing the comparator 72 to generate an outputsignal which causes transistor 77 to conduct, energizing the coil ofrelay 78, which causes the contacts 64 to switch from the position shownin FIG. 6 and reverse the current in actuator A1, designated 63. Thisreverses the direction of the actuator.

Thus, when the target light source is directly incident on a primarysensor, the associated actuator extends, and when the light source doesnot illuminate a sensor, the associated actuator retracts.

The All-Stop Circuit shown in FIG. 7 is similar to the driver circuitsfor the actuators in configuration, components and operation. However,the primary sensor 39 is the All-Stop (or “target acquired”) sensordiscussed above. Hence, similar reference numerals are used for the samecomponents. However, the output relay is designated 78A in FIG. 7; andit actuates a simple contact 79 which, when in the position shown inFIG. 7 to disable all three actuators. The ambient balance for the “allstop” circuit if FIG. 7 is connected to ground by Connection 82 inparallel to the Connections at 79, 80, and 81 for each actuator circuitas shown in FIG. 6. This disables the actuator controllers by groundingjunction 71 (i.e., B1) in FIG. 6 during periods of darkness.

When that “all stop” sensor 40 is illuminated directly (i.e. the sourceis directly overhead of the sighting recess 42 and along the sightaxis), the comparator 72 causes transistor 77 to conduct and all threeactuators 9, 10 and 11 (A1, A2 and A3) are disconnected from theirassociated power source. When the light source is not aligned with thesight axis, the “All Stop” circuit is not enabled, and all threeactuators are supplied with power and ready to act.

Although the illustrated embodiment has each sector of the sensor arrayextending an equal angular increment, this is preferred, but notnecessary. For example, one sector could extend for sixty degrees andthe other two for one hundred and fifty degrees each. Even these angularrelations may be changed, and the final angles may be affected by theparticular application. Moreover, the triangle formed by the mountinglocations of the actuators need not be equilateral. However, the supportcolumn should be mounted to the center of the triangle—that is, thepoint at which lines which bisect the three angles intersect. Othermountings forming a triangle include the floating base. Sensors mayinclude photo resistors, photo diodes, motion sensors or heated fluids.

1. Apparatus for tracking a light source comprising: a support column; aplatform rotatably mounted to said support column and having a sightaxis extending perpendicular from said platform; a base slidablyreceived on said support column for motion along an axis thereof; aplurality of linear actuators equally angularly spaced about saidcolumn, each actuator rotatably mounted at one location to said platformand rotatably mounted at a second location to said base; at least onesensor for each actuator, each sensor responsive to incident radiantenergy, said sensors arranged to directly receive energy from said lightsource in different lateral sectors of said platform when said sightaxis intersects the light source and not having line-of-sight access toany other of said sensors; and a controller for each associated sensorand actuator, each controller generating a signal to extend anassociated actuator when incident radiant energy above a predeterminedlevel is received by said sensor and to retract when incident radiantenergy is below said predetermined level.
 2. The apparatus of claim 1comprising three sensors and three linear actuators, each having a rodend and a butt end; a spherical joint connecting one of said rod end andbutt end of an actuator to said platform; and a spherical jointconnecting the other of said rod end and butt end of each actuator tosaid base.
 3. The apparatus of claim 2 comprising three linearactuators, each actuator rotatably connected to said platform at amounting location, said mounting locations defining an equilateraltriangle.
 4. The apparatus of claim 2 further comprising an opaque wallseparating each sensor from direct line of sight with adjacent sensorswhile not restricting direct incidence of radiant energy along pathsparallel to said sight axis of said platform.
 5. The apparatus of claim4 wherein said sensors are primary sensors for reception of directsource radiation, and further comprising an ambient sensor for eachprimary sensor for detecting ambient radiation, and wherein said opaquewall includes three wall segments extending radially out from a centrallocation and defining three equal sensor segments, a primary sensorbeing located in each sensor segment adjacent the location where twoadjacent wall segments meet and at the base of said wall; and whereineach ambient sensor is located in a recess at the base of one of saidwall segments for receiving radiation only from a direction radiallyextending from said sight axis.
 6. The apparatus of claim 1 furtherincluding second and third sensors located in separate sectors of equalangular extension, further including an opaque barrier including threepartial walls, one wall located between each pair of adjacent sensorsand precluding line-of-sight access between adjacent sensors.
 7. Theapparatus of claim 1 wherein each of said sensors is a photoresistorcomprising a primary sensor, said apparatus further including an ambientsensor for each primary sensor, each ambient sensor housed to receiveambient light while precluded from direct viewing along lines parallelto said sight axis, and wherein each controller includes a comparatorcircuit for comparing the response signal of a primary sensor with theresponse signal of an associated ambient sensor, the primary sensorgenerating a control signal for an associated actuator only when itsinput signal is greater than the associated ambient signal.
 8. Theapparatus of claim 1 further comprising a target-acquired sensor mountedin a recess extending along a center line in the direction of the sightaxis of the carrier platform, said controller generating a signal tostop further movement of said actuators when said target acquired sensorreceives directly radiation from the target.
 9. The apparatus of claim 1further comprising a hinge for mounting said platform to said column forrotation only about two orthogonal axes.
 10. The apparatus of claim 5wherein each actuator is arranged to elevate said carrier platform at alocation opposite the sensor associated with the actuator when theactuator is extended, and to lower said carrier platform at saidlocation opposite the associated sensor when the actuator is retracted.